The present invention relates to an apparatus for promoting the vaporization of liquid fuel in an internal combustion engine.
The low engine temperature before completion of engine warm-up results in insufficient vaporization of the fuel supplied from the carbureter. The supply of a large quantity of the fuel into the engine cylinders in the liquid state, results in poorer than after completion of warm-up, whereby stable operation of the engine cannot be obtained. Accordingly, during warm-up, an air-fuel mixture which is richer than the air-fuel mixture used after completion of warm-up is supplied into the engine cylinders so as to maintain stable engine operation. However, the supply of such a richer air-fuel mixture to the engine cylinder causes not only an increase in the amount of poisonous components such as unburnt hydrocarbons HC and carbon monoxide gas CO in the exhaust but also the reduction of the fuel consumption. Accordingly, the sufficient vaporization of the liquid fuel supplied from the carburetor during engine warm-up would enable stable engine operation even with a reduced air-fuel mixture. The use of such a reduced air-fuel mixture would allow the control of the formation of poisonous components in the exhaust gas and the increase of the fuel consumption. We previously proposed an intake heating apparatus for promoting vaporization of a liquid fuel during engine warm-up, which comprises a hollow heating element vessel attached to, for example, the outlet portion of a carbureter air horn, said hollow heating element vessel including an inner pipe, an outer pipe, and a plurality of positive temperature coefficient thermistors (hereinafter referred to as "PTC elements") inserted between the inner and outer pipes, wherein the inner pipe of the hollow heating element vessel is heated by heating the PTC elements. In this intake heating apparatus, in order to prevent formation of short circuits by electric contact between the front surface and back surface of the PTC element and also to prevent cracking of the PTC elements by oscillation, an insulating member is inserted in the gap between adjacent PTC elements, or a resinous adhesive is filled in the gap between the adjacent PTC elements. However, the insertion of insulating members or filling of resinous adhesive are time- and labor-consuming operations and lack reliability, therefore making an such intake heating apparatus not satisfactory for practical purposes.